Method and system for optimizing parallel program execution based on speculation that an object written to is not shared

A method for executing a program in parallel includes creating a program replica, which includes a write operation on and an identifier of an object and is a copy of the program, for a thread. The identifier specifies whether the object is thread-local. The method includes modifying the write operation based on a speculation that the write operation uses only thread-local objects. The write operation executes in a transaction of the thread. The method includes determining, while executing the program replica and using the identifier, that the object used by the write operation is not thread-local, de-optimizing the write operation by adding instrumentation to implement a software transactional memory (STM) system for the write operation to obtain a de-optimized write operation, and performing the de-optimized write operation on the object to obtain a result and store the result in a redo log.